Low-frequency one-electrode discharge in long tubes at low gas pressure

Abstract

One electrode discharge (OED) was studied in long tubes filled with high purity neon or argon at a pressure of 1-4 Torr. The main feature of the discharge is a low rate (less than 10 kHz) of the voltage pulses of given polarity applied to only one electrode, while another one remains free or missing. The discharge is observed as a glowing plasma column which occupies either the whole tube or its part depending on actual voltage amplitude and rate. Current-volt characteristics, ignition thresholds and the OED length changing patterns demonstrate features unknown for RF discharges. It was found that the plasma generation mechanism actually is a formation of a set of ionization waves (IW). As a result, the discharge glow as well as its current can be presented as a set of pulses with duration equal to the IW propagation time (∼1 μs) that appear with the voltage frequency. The pulse form reflects the IW structure which represents itself as a front of high electrical potential and a plasma channel linking it with the electrode. It was shown that the wave motion is characterized by an attenuation of which the patterns were investigated by the time-position diagrams method. The attenuation specifies the length of the occupied plasma area as well as other OED parameters. The proposed simplified kinematic model of the wave propagation is based on the assumption that the attenuation is caused by the IW front potential decrease which in its turn occurs due to exponential falling of electric field strength in the plasma channel. This model allows to estimate the electric field in different OED points as well as to define average electron concentration via the current measurements. Typical values of the above parameters are 5 V cm−1 · Torr and 109-1010 cm−3.